Covering material

ABSTRACT

The present invention provides a covering material having a layer formed of a resin of which glass transition point is in the range of 10° C. to 50° C., said covering material having excellent shape keeping ability and shape recovering ability after deformation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a plastic covering materialhaving excellent shape keeping ability for sealing containers such ascup, bowl and tray formed of paper, synthetic resin and the like.

[0003] 2. Description of the Prior Art

[0004] Conventionally, as materials for a covering material which isbonded to an opening of a container made of paper, synthetic resin andthe like for accommodating beverages, portions, foods such as instantnoodles, or medical devices such as disposable contact lens for sealingthe container, aluminum foils and polypropylene polymers have beenwidely used.

[0005] The reason why aluminum foils are used in the covering materialas described above is that in addition to shielding the light and airthereby protecting the contents, the covering material has ability tokeep a turned-up shape (shape keeping ability) in the case where thecovering material is partly torn off and then the contents are takenfrom the container or hot water is poured into the container.

[0006] As an alternative of such conventional covering materials havingaluminum foil layer, a covering material formed of a plastic in itsentirety has been proposed. For example, in Japanese Unexamined PatentPublication JP 11-101810-A (1999), a covering material which is formedby punching a laminated material into a predetermined shape isdisclosed, the laminated material being configured by laminating heatresistant films on both sides of a base material of a co-extruded filmhaving a center layer made of high-density polyethylene andpolypropylene-based polymer and coating layers made of high-densitypolyethylene on both sides of the center layer to make a lamination basematerial, and providing a sealant layer on the bottom surface of thelamination base material. However, such conventional plastic coveringmaterials did not have sufficient shape keeping ability. That is, theability of the conventional covering materials to keep the deformedcondition when they are deformed, for example, by bending was notsatisfactory. Furthermore, the conventional covering materials did nothave sufficient shape recovering ability after deformation. That is, itwas difficult for the conventional covering materials to recover thecondition before deformation without causing damages such as foldingwrinkles.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a plasticcovering material having excellent shape keeping ability and shaperecovering ability after deformation.

[0008] As the result of researches for developing a plastic coveringmaterial having excellent shape keeing ability and shape recoveringability after deformation, the inventors of the present invention foundthat a covering material having a layer formed of a resin of which glasstransition oint is in the range of 10° C. to 50° C. satisfies theabove-mentioned object and accomlished the present invention.

[0009] Further scope of applicability of the present invention willbecome apparent from the detailed descrition given hereinafter. However,it should be understood that the detailed description and specificexamples, while indicating referred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed descrition.

[0010] Throughout this specification and the claims which follow, unlessthe context requires otherwise, the word “comprise”, and variations suchas “comprises” and “comprising”, will be understood to imply theinclusion of a stated integer or step or group of integers or steps butnot the exclusion of any other integer or step or group of integer orstep.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic view for explaining procedure of a shapekeeping test (1) of covering material; and

[0012]FIG. 2 is a schematic view for explaining procedure of a shapekeeping test (2) of covering material.

DETAILED DESCRIPTION OF THE INVENTION

[0013] A covering material of the present invention is characterized byhaving a layer formed of a resin of which glass transition point is inthe range of 10° C. to 50° C.

[0014] Glass transition point (hereinafter, also referred to as Tg)means the boundary temerature that a resin being heated transits fromthe glass state to the rubber state, and is observed as an inflectionpoint of a DSC curve which corresponds to the step-wise change in thespecific heat capacity in measurement using a differential scanningcalorimeter (DSC).

[0015] The covering material of the present invention has a layer formedof a resin of which glass transition point is in the range of 10° C. to50° C., with the result that it is excellent in the shape keepingability. The glass transition point is referably in the range of 15° C.to 45° C., more referably in the range of 20° C. to 45° C., and mostpreferably in the range of 25° C. to 40° C.

[0016] It is preferred that the resin of which glass transition point isin the range of 10° C. to 50° C. is an amorhous resin from the viewpoint of the shape recovering ability after deformation. The coveringmaterial having a layer formed of an amorhous resin of which glasstransition point is in the range of 10° C. to 50° C. is excellent inshape recovering ability. That is, even if the sheet is folded, it canrecover the condition before the folding without leaving any wrinkles.Incidentally, when an endothermic peak or a melting point is notobserved in measuring a resin using a differential scanning calorimeter(DSC), the resin is judged as amorhous.

[0017] In the present invention, structure of the resin of which glasstransition point is in the range of 10° C. to 50° C. is not particularlylimited, and the resin may be copolymers formed by polymerizing (a)ethylene and/or α-olefin and (b) cyclic olefin and/or alkenyl aromatichydrocarbon. The glass transition point of such a resin may be adjustedin the range of 10° C. to 50° C. by changing the copolymerizationcomposition of the resin.

[0018] The above-mentioned “ethylene and/or α-olefin” means either oneof ethylene alone, α-olefin alone or combination of ethylene andα-olefin, with ethylene alone being particularly referred. Further, theabove-mentioned “cyclic olefin and/or alkenyl aromatic hydrocarbon”means either on of cyclic olefin alone, alkenyl aromatic hydrocarbonalone, or combination of cyclic olefin and alkenyl aromatic hydrocarbon.

[0019] As the α-olefin in the coolymer, α-olefins having from 3 to 20carbon atoms are preferred. Typically, examples thereof include linearα-olefins such as proylene, butene-1, pentene-1, hexene-1, hetene-1,octene-1, nonene-1 and decene-1, branched α-olefins such as3-methylbutene-1, 3-methylpentene-1, 4-methylpentene-1 and5-methyl-hexene-1, vinylcyclohexane and the like. More preferredα-olefins are proylene, butene-1, pentene-1, hexene-1, heptene-1,octene-1, 4-methylpentene-1 and vinylcyclohexane. Among them, proyleneis particularly preferred.

[0020] α-olefin may be used alone or in combination of two or morekinds.

[0021] In the copolymers formed by polymerizing (a) ethylene and/orα-olefin and (b) cyclic olefin and/or alkenyl aromatic hydrocarbon, thecyclic olefin refers to a compound having a ring consisting of 4 or morecarbon atoms and including one carbon-carbon double bond in the ring.Such cyclic olefin may have various kinds of substituents. Examples ofsuch cyclic olefin include: monocyclic olefins such as cyclobutene,cycloentene, cyclohexene and cyclooctene; substituted monocyclic olefinssuch as 3-methylcycloentene, 4-methylcyclopentene and3-methylcyclohexene; polycyclic olefins such as norbornene,1,2-dihydrodicyclopentadiene and tetracyclododecene; and substitutedpolycyclic olefins such as 5-methylnorbornene.

[0022] Preferred cyclic olefins among these are compounds represented bythe following general formula [IV].

[0023] (Wherein R⁷ to R¹⁸ indeendently reresent hydrogen atom, hydroxylgroup, amino group, phosphino group, or organic group having 1-20 carbonatoms, and R¹⁶ and R¹⁷ may be bonded to each other to form a ring. “m”reresents an integer of 0 or more.)

[0024] Concrete examples of the organic group having 1 to 20 carbonatoms which is one member of the substituents include: alkyl groups suchas methyl group, ethyl group, propyl group, butyl group, hexyl group,octyl group and dodecyl group; aryl groups such as phenyl group, tolylgroup and naphthyl group; aralkyl groups such as benzyl group andphenetyl group; alkoxy groups such as methoxy group and ethoxy group;aryloxy groups such as henoxy group; acyl groups such as acetyl group;alkoxycarbonyl groups such as methoxycarbonyl group and ethoxycarbonylgroup; aryloxycarbonyl groups such as phenoxycarbonyl group;aralkyloxycarbonyl groups such as benzyloxycarbonyl group; acyloxygroups such as acetyloxy group; alkoxysulfonyl groups such asmethoxysulfonyl group and ethoxysulfonyl group; aryloxysulfonyl groupssuch as phenoxysulfonyl group; aralkyloxysulfonyl groups such asbenzyloxysulfonyl group; substituted silyl groups such as trimethylsilylgroup; dialkylamino groups such as dimethylamino group and diethylaminogroup; carboxyl groups; cyano groups; and groups in which art ofhydrogen atoms of said alkyl groups, aryl groups and aralkyl groups aresubstituted by hydroxyl groups, amino groups, acyl groups, carboxylgroups, alkoxy groups, alkoxycarbonyl groups, acyloxy groups,substituted silyl groups, alkylamino groups or cyano groups.

[0025] Preferably, R⁷ to R¹⁸ are independently hydrogen atom, alkylgroups having 1-20 carbon atoms, aryl groups having 1-20 carbon atoms,aralkyl groups having 7-20 carbon atoms; acyl groups having 1-20 carbonatoms, alkoxycarbonyl groups having 1-20 carbon atoms, acyloxy groupshaving 1-20 carbon atoms or di-substituted silyl groups having 1-20carbon atoms.

[0026] m is an integer of 0 or more, and referably an integer in therange of 0≦m≦3.

[0027] Concrete examles of cyclic olefin represented by the generalformula [IV] include norbornene, 5-methylnorbornene, 5-etylnorbornene,5-butylnorbornene, 5-phenylnorbornene, 5-benzylnorbornene,tetracyclododecene, tricyclodecene, tricycloundecene,pentacyclopentadecene, pentacyclohexadecene, 8-methyltetracyclododecene,8-ethyltetracyclododecene, 5-acetylnorbornene, 5-acetyloxynorbornene,5-methoxycarbonylnorbornene, 5-ethoxycarbonylnorbornene,5-metyl-5-methoxycarbonylnorbornene, 5-cyanonorbornene,8-methoxycarbonyltetracyclododecene, 8-methyl-8-tetracyclododecene,8-cyanotetracyclododecene and the like.

[0028] In polymerization, these cyclic olefins may be used alone or inplural.

[0029] In the above-mentioned copolymers formed by polymerizing (a)ethylene and/or α-olefin and (b) cyclic olefin and/or alkenyl aromatichydrocarbon, the alkenyl aromatic hydrocarbon is referably compoundsrepresented by the following general formula [V].

[0030] (wherein R¹⁹ represents a hydrogen atom or alkyl groups having1-20 carbon atoms, and Ar represents aromatic hydrocarbon groups having6-25 carbon atoms.)

[0031] R¹⁹ is a hydrogen atom or alkyl groups having 1-20 carbon atoms,and concrete example of the alkyl groups having 1-20 carbon atomsinclude methyl group, ethyl group, propyl group, butyl group, hexylgroup, octyl group, dodecyl group and the like. R¹⁹ is preferably ahydrogen atom or methyl group.

[0032] Ar is aromatic hydrocarbon groups having 6-25 carbon atoms, andconcrete examples of the aromatic hydrocarbon groups having 6-25 carbonatoms include phenyl group, tolyl group, xylyl group, tertiarybutylphenyl group, vinylphenyl group, naphthyl group, phenanthryl group,anthracenyl group, benzyl group and the like. Phenyl group, tolyl group,xylyl group, tertiary butylphenyl group, vinylphenyl group or naphthylgroup is preferred.

[0033] Concrete examles of the alkenyl aromatic hydrocarbon include:alkylstyrenes such as p-methylstyrene, m-methylstyrene, o-methylstyrene,p-ethylstyrene, m-ethylstyrene, o-ethylstyrene, 2,4-dimethylstyrene,2,5-dimethylstyrene, 3,4-dimethylstyrene, 3,5-dimethylstyrene,3-methyl-5-ethylstyrene, p-tertiary butylstyrene and p-secondarybutylstyrene; alkenylbenzenes such as styrene, 2-henylpropyrene,2-phenylbuthene and 3-phenylpropyrene; bisalkenylbenzenes such asdivinylbenzen; and alkenylnaphthalenes such as 1-vinylnaphthalene. Asthe alkenyl aromatic hydrocarbon, styrene, p-methylstyrene,m-methylstyrene, o-methylstyrene, p-tertiary butylstyrene,2-phenylpropyrene, or 1-vinylnaphthalene is preferred, and styrene isparticularly preferred.

[0034] In the present invention, preferred resins as the resin having aglass transition point in the range of 10° C. to 50° C. are: copolymersof (a) ethylene and/or α-olefin and (b1) cyclic olefin; copolymers of(a) ethylene and/or α-olefin and (b2) alkenyl aromatic hydrocarbon; andcopolymers of (a) ethylene and/or α-olefin and both of (b1) cyclicolefin and (b2) alkenyl aromatic hydrocarbon, with copolymers ofethylene and/or α-olefin and both of (b1) cyclic olefin and (b2) alkenylaromatic hydrocarbon being particularly preferred.

[0035] In a copolymer containing cyclic olefin as a copolymerizationcomponent, copolymerization composition of the cyclic olefin ispreferably in the range of 0.01 to 40 mol %. In the case where thecopolymerization composition of the cyclic olefin falls within thisrange, the copolymer is excellent particularly in oil resistance andheat resistance. The copolymerization composition of the cyclic olefinis more preferably in the range of 0.1 to 30 mol %, and most preferablyin the range of 1 to 20 mol %. The copolymerization composition ofcyclic olefin can be readily determined by ¹H-NMR sectrum or 13C-NMRspectrum.

[0036] In a copolymer containing alkenyl aromatic hydrocarbon as acopolymerization component, copolymerization composition of the alkenylaromatic hydrocarbon is preferably in the range of 1 to 70 mol %. In thecase where the copolymerization composition of the alkenyl aromatichydrocarbon falls within this range, the copolymer is excellentparticularly in heat resistance and flexibility and has high refractiveindex. The copolymerization composition of the alkenyl aromatichydrocarbon is more preferably in the range of 3 to 55 mol %, and mostpreferably in the range of 5 to 45 mol %. The copolymerizationcomposition of alkenyl aromatic hydrocarbon can be readily determined by¹H-NMR sectrum or ¹³C-NMR spectrum.

[0037] In a copolymer of (a) ethylene and/or α-olefin and both of (b1)cyclic olefin and (b2) alkenyl aromatic hydrocarbon that may be used inthe present invention, copolymerization composition of the alkenylaromatic hydrocarbon is preferably more than a half of copolymerizationcomposition of the cyclic olefin. The copolymerization composition ofthe alkenyl aromatic hydrocarbon is more preferably more than or equalto the copolymerization composition of the cyclic olefin. In the casewhere the copolymerization composition of the alkenyl aromatichydrocarbon falls within this range, the copolymer is excellent inbalance of solvent resistance, heat resistance and flexibility.

[0038] In the present invention, as the resin having a glass transitionpoint in the range of 10° C. to 50° C., copolymers in which diene iscopolymerized in addition to ethylene and/or α-olefin, cyclic olefin,and alkenyl aromatic hydrocarbon may be used. As such diene, bisalkenylaromatic hydrocarbon, cyclic diene, linear diene, branched diene and thelike can be exemplified, however, bisalkenyl aromatic hydrocarbon,cyclic diene and branched diene are preferred, bisalkenyl aromatichydrocarbon and cyclic diene are more preferred, and among thembisalkenyl aromatic hydrocarbon is most preferred. As the bisalkenylaromatic hydrocarbon, divinylbenzene, divinylnaphthalene,divinylbiphenyl, diallylbenzene and the like can be exemplified. As thecyclic diene, norbornadiene, dicyclopentadiene, vinylnorbornene,vinylcyclohexene, ethylidene norbornene and the like can be exemplified.As the linear diene, 1,5-hexadiene, 1,7-octadiene and the like can beexemplified. As the branched diene, isorene and the like can beexemplified.

[0039] In the present invention, as the resin having a glass transitionpoint in the range of 10° C. to 50° C., copolymers in which other vinylcompound is copolymerized in addition to ethylene and/or α-olefin,cyclic olefin, and alkenyl aromatic hydrocarbon may be used. Concreteexamples of such vinyl compound include methylvinylether,ethylvinylether, acrylic acid, methyl acrylate, methyl methacrylate,acrylonitrile, vinyl acetate and the like.

[0040] There is no particular limitation in the process for producingthe copolymer of (a) ethylene and/or an α-olefin and (b) a cyclic olefinand/or an alkenyl aromatic hydrocarbon in the resent invention. Theremay be applied various kinds of methods, for example, a gas phasepolymerization in a batch or continuous system, a bulk polymerizationmethod, a solution or slurry polymerization method using an adequatesolvent. As a polymerization catalyst, for example, non-uniform Zieglercatalysts, metallocene-based catalysts disclosed in Japanese PatentLaid-Open Publications No. Hei-3-250007, Hei 7-70223, Hei 9-309925, Hei9-87313 and Hei 9-183809, WO98/09999, non-metallocene catalysts andthese like metal catalysts and the like may be used, but the catalyst isnot restricted to these ones. In the polymerization, a chain transferagent such as hydrogen may be used for the purpose of the adjustment ofa molecular weight of the copolymer.

[0041] As the above metal catalysts are used metallocene-basedcatalysts, and among them a catalyst prepared from the followingtransition metal comlex (A), the following Aluminum compound (B) and/orthe following Boron compound (C) is particularly more preferred.

[0042] (A): The transition metal complex represented by the followinggeneral formulas [I], [II] or [III]:

[0043] In the general formulas [I], [II] and [III], M¹ represents atransition metal atom of Group 4 of the Periodic Table of Elements, Arepresents an atom of Group 16 of the Periodic Table of Elements, Jrepresents an atom of Group 14 of the Periodic Table of Elements, and Crepresents a group having a cycloentadiene-type anion skeleton. X¹, X²,R¹, R², R³, R⁴, R⁵ and R⁶ independently reresent a hydrogen atom, ahalogen atom, an alkyl group, an aralkyl group, an aryl group, asubstituted silyl group, an alkoxy group, an aralkyloxy group, anaryloxy group or a di-substituted amino group. X³ represents an atom ofGroup 16 of the Periodic Table of Elements. R¹, R², R³, R⁴, R⁵ and R⁶may arbitrarily be combined to form a ring. The two M¹s, As, Js, Cp¹s,X¹s, X²s, X³s, R¹s, R²s, R³s, R⁴s, R⁵s or R⁶s in the general formula[II] or [III] may be either the same or different. (B): At least onealuminum compound selected from the following (B1) to (B3):

[0044] (B1) An organoaluminum compound represented by the generalformula E¹ _(a)AlZ_(3-a)

[0045] (B2) A cyclic aluminoxane having a structure represented by thegeneral formula {—Al(E²)—◯—}_(b)

[0046] (B3) A linear aluminoxane having a structure represented by thegeneral formula E³{—Al(E³)—◯—}_(c)AlE³ ₂

[0047] In the above general formulas, E¹, E² and E³ each indicates ahydrocarbon group, and all E¹s, all E²s and all E³s may be either thesame or different. Z represents a hydrogen atom or a halogen atom andall Zs may be either the same or different. The character “a” representsa number satisfying 0<a≦3, b represents an integer not smaller than 2,and c represents an integer not smaller than 1.

[0048] (C): A boron compound selected from the following (C1) to (C3):

[0049] (C1) A boron compound represented by the general formula BQ¹Q²Q³

[0050] (C2) A boron compound represented by the general formula G+(BQ¹Q²Q³Q⁴)

[0051] (C3) A boron compound represented by the general formula (L-H) +(BQ¹Q²Q³Q⁴)

[0052] In the general formulas, B represents a trivalent boron atom, Q¹to Q⁴ each represents a halogen atom, a hydrocarbon group, a halogenatedhydrocarbon group, a substituted silyl group, an alkoxy group or adi-substituted amino group and may be either the same or different, G+isan inorganic or organic cation, L is a neutral Lewis base, and (L-H)+isa Brensted acid.

[0053] (A) Transition metal complex

[0054] The transition metal complex represented by the general formula[I] may be reared, for example, by the method disclosed in WO97/03992-A.The transition metal complexes represented by the general formulas [II]and [III], respectively, may be prepared by reacting the transitionmetal complex represented by the general formula [I] with water in anamounts of 0.5 molar time and 1 molar time that of the transition metalcomlex [I]. In their rearation, there may be applied, for example, amethod wherein the transition metal complex represented by the generalformula [I] is directly reacted with a required amount of water and amethod wherein the transition metal complex represented by the generalformula [I] is ut into a dry solvent such as hydrocarbons and is furtherpassed through an inert gas and the like containing a required amount ofwater.

[0055] (B) Aluminum compound

[0056] Examples of the aluminum compound (B) include triethylaluminum,triisobutylaluminum, methylaluminoxane and other alkylalmoxanes.

[0057] (C) Boron compound

[0058] Examples of the boron compound (C) include triphenylmethyltetrakis(pentafluorophenyl)borate, tri(n-butyl)ammoniumtetrakis(pentafluorophenyl)borate and N, N-dimethylaniliniumtetrakis(pentafluorophenyl)borate.

[0059] In the present invention, the resin having a glass transitionpoint in the range of 10° C. to 50° C. may contain talc, antioxidant,anti-weathering agent, lubricant, anti-blocking agent, antistatic agent,anti-blooming agent, non-dropping agent, coloring agent, filler and thelike as appropriate. Furthermore, insofar as the effect of the presentinvention is deteriorated, the resin may contain polymer substances byradical polymerization such as low-density polyethylene, high-densitypolyethylene, linear low-density polyethylene, ethylene/α-olefinelastomer, polyroylene, polystyrene and the like as appropriate.

[0060] As described above, the covering material of the presentinvention having a layer formed of a resin of which glass transitionpoint is in the range of 10° C. to 50° C. is normally in the form ofsheet or film, however, there is no special limitation for the thicknessthereof.

[0061] Since the layer formed of the specific resin is excellent in theshape keeping ability and the shape recovering ability, the coveringmaterial of the present invention is excellent in the shape keepingability and the shape recovering ability. The covering material of thepresent invention may be composed of only the layer formed of a resin ofwhich transition point is in the range of 10° C. to 50° C. For example,a single-layer sheet formed of a copolymer of (a) ethylene and/orα-olefin and (b2) alkenyl aromatic hydrocarbon, and a single-layer sheetformed of a copolymer of (a) ethylene and/or α-olefin and both of (b1)cyclic olefin and (b2) alkenyl aromatic hydrocarbon exhibit excellentheat seal property with respect to a container in which at least itssurface is formed of polystyrene or polyethylene, so that suchsingle-layer sheets may be used as a covering material as they are.

[0062] Furthermore, the covering material of the present invention maybe a laminate having an approriate sealant layer. Also, insofar as theeffect of the present invention is not significantly deteriorated, thecovering material of the present invention may have other layers (forexample, adhesive layer, heat resistant protecting layer, printinglayer, gas-barrier layer, light resistant layer and the like) inaddition to the layer of the above-mentioned resin having a transitionpoint in the range of 10° C. to 50° C. and sealant layer. As a materialfor the heat resistant protecting layer, poly(ethylene terephthalate),nylon, polyroylene and the like can be exemplified. As a material forthe gas-barrier layer, poly(vinylidene chloride), saponifiedethylene/vinyl acetate copolymer and the like can be exemplified. Lightresistant layer refers to a layer intended for shielding visible lightand ultraviolet light, and examples of the light resistant layer includea synthetic resin layer having inorganic articles such as titanium oxideparticles, paper layer, ink layer, vapor deposition layer and the like.

[0063] The single-layer covering material formed of a resin having aglass transition point in the range of 10° C. to 50° C. may be producedaccording to various kinds of methods including inflation method, T diemethod, pressing method.

[0064] The covering material comprising a laminate including a layer ofa resin having a glass transition point in the range of 10° C. to 50° C.may be produced according to the inflation method, T die method,pressing method and the like by co-extrusion. Also it may be possible toproduce the covering material by laminating films for respective layerswhich are produced separately, according to the dry lamination methodusing two-liquid reactive adhesive or the sandwich lamination method andthe like. Each film for resective layers of the laminate may be producedaccording to various kinds of methods such as inflation method, T diemethod, pressing method and the like.

[0065] The covering material of the resent invention, when deformed bythe action of the external force, expresses excellent shape keepingability to keep the deformed condition, and exhibits excellent shaperecovering ability after deformation.

EXAMPLES

[0066] In the following, the present invention will be explained withreference to the examples, however, the present invention is not limitedto the examples.

[0067] Test methods <Shape keeping test (1)>

[0068] At 23° C., a test piece 1 cut out into a 50 mm square of 0.3 mmin thick was bent on the base with fingers, and kept for 10 seconds[FIG. 1(A)]. Next, 10 seconds and 1 minute after moving the fingers offthe test piece, the bent angle A was measured [FIG. 1(B)]. The largerthe bent angle A, the more excellent the shape keeping ability is.

[0069] <Shape keeping test (2)>

[0070] A test piece (cap) 2 cut into a circle having a diameter of 70 mmand a thickness of 0.3 mm, and a lastic (polystyrene or polypropylene)lower container 3 having a circular oening of an inside diameter of 62mm which is surrounded by a flange portion of 3 mm in width wereprepared. The test piece was heat sealed at 180° C. on the flangeportion of the lower container, thereby creating a sealed container 4[FIG. 2(A)]. One end of the test piece [the point T in FIG. 2(B)] waspicked while the lower container being fixed; the test piece was peeledoff the lower container by pulling the test piece in the direction of45° with respect to the unpeeled art of the test piece, and the sealedcontainer was opened up to the mid art of the opening of the lowercontainer [FIG. 2(B)]. After oening, the bent angle A′ of the test piecewhich was released from the external force was measured [FIG. 2(C)]. Thelarger the bent angle, the more excellent the shape keeping ability.

[0071] <Glass transition point and melting point of resin>

[0072] Glass transition point (Tg) and melting oint (TM) were measuredusing a differential scanning calorimeter (DSC) (SSC-5200, manufacturedby Seiko Instruments Inc.) under the conditions as follows:

[0073] Preheating: Heat from 20° C. to 200° C. (20° C./min.), Retain at200° C. for 10 minutes

[0074] Precooling: Cool from 200° C. to −50° C. (20° C./min.), Retain at−50° C. for 10 minutes

[0075] Measuring: Heat from −50° C. to 300° C. (20° C./min.)

[0076] <Content of units from styrene in resin and resin structure>

[0077] Content of units from styrene in a copolymer and the structure ofthe copolymer were determined by ¹³C-NMR (JNM-EX270, manufactured byJEOL Ltd.) analysis.

[0078] Measuring solvent: 85:15 (weight ratio) mixture ofo-dichlorobenzene and heavy benzene.

[0079] Measuring temerature: 135° C.

[0080] <Solid dynamic viscoelasticity>

[0081] Solid dynamic viscoelasticity of resin was determined using asectrometer (Measurement Analyzer LEO STATION SDM5600H manufactured bySeiko Instruments Inc. connected with a Tension Module DMS200) under theconditions as follows:

[0082] Test piece: press sheet of 20 mm×3.0 mm×0.3 mm

[0083] Frequency: 5 Hz

[0084] Heating seed: 2° C./min.

[0085] Dislacement amlitude: 10 μm

Example 1

[0086] In a 100 mL autoclave relaced by argon, 15 ml of dehydratedtoluene, 1.0 ml (1 mmol) of triisobutylaluminum solution in toluene [1mol/l, manufactured by Tosoh Akzo Co. Ltd.], 1.5 mg (4 μmol) ofisoroylidene (cyclopentadienyl) (3-tert-butyl-5-methyl-2-phenoxy)titanium dichloride dissolved in 1.5 ml of dehydrated toluene, 11.1 mg ofphenylmethyltetrakis(pentafluorophenyl) borate dissolved in 2.4 ml ofdehydrated toluene (12 μmol), and 20 ml of styrene were sequentiallyadded, and finally 2 kg/cm² of ethylene was supplied. After stirring thereaction mixture at 60° C. for 1 hour, the reaction mixture was put intoa mixture of 1 ml hydrochloride (12N) and 300 ml methanol andprecipitated white solid was obtained by filtering. After washing thesolid with methanol, vacuum dry of the solid resulted in 1.89 g ofpolymer (ethylene/styrene copolymer). Glass transition point of thispolymer was 34° C., with its melting oint substantially not confirmed,and content of units from styrene was 50 mol %. From measurement ofsolid dynamic viscoelasticity, the maximum value of tan δ was 1.99.

[0087] Using this resin, a 0.3 mm thick sheet was produced by a tabletoppress machine. The shape keeping ability test (1) and the shape keepingability test (2) were carried out for this sheet. The results are shownin Table 1. As the lower container, a polystyrene container was used. Itwas proved that this sheet is excellent in the shape keeping ability.Moreover, when the test piece bent in the shape keeping ability test (1)was recovered to the original condition before bending, the test piecerecovered the shape before bending without causing wrinkles at the bentportion.

Example 2

[0088] In a 400 mL autoclave replaced by argon, after preliminarilyintroducing 46 ml of styrene, 4 ml of norbornene solution in toluene (5mol/l) and 102 ml of dehydrated toluene, 0.8 MPa of ethylene wassupplied. To this mixture, a mixture consisting of 3.0 ml oftriisobutylaluminum solution in toluene [1 mol/l, manufactured by TosohAkzo Co. Ltd.] and a solution obtained by dissolving 15.5 mg ofisopropylidene(cyclopentadienyl)(3-tert-butyl-5-methyl-2-phenoxy)titanium dichloride in 15 ml of dehydrated toluene was added, then a solutionobtained by dissolving 96.1 mg ofN,N-dimethylaniliniumtetrakis(pentafluorohenyl) borate in 30 ml ofdehydrated toluene was added, and the reaction mixture was stirred at60° C. for 2 hours. Thereafter the reaction mixture was ut into amixture of 5 ml hydrochloride (12N) and 1000 ml acetone and precipitatedwhite solid was obtained by filtering. After washing the solid withacetone, vacuum dry of the solid resulted in 32.82 g of polymer(ethylene/styrene/norbornene copolymer). Glass transition point of thispolymer was 27° C., content of units from styrene was 39 mol %, andcontent of units from norbornene was 3 mol %.

[0089] Using this resin, a 0.3 mm thick sheet was produced by a tabletoppress machine. The shape keeping ability test (1) and the shape keepingability test (2) were carried out for this sheet. The results are shownin Table 1. In the shape keeping ability test (2), a polystylenecontainer was used as the lower container. It was proved that this sheetis excellent in the shape keeping ability. Moreover, when the test piecebent in the shape keeping ability test (1) was recovered to the originalcondition before bending, the test piece recovered the shape beforebending without causing wrinkles at the bent portion.

Comparative Example 1

[0090] Using a propylene/ethylene random copolymer (SUMITOMO NOBLEN®RS160XG manufactured by Sumitomo Chemical Co. Ltd., Tm=135° C., Tg=−1°C.), a 0.3 mm thick sheet was roduced by a tabletop press machine. Theshape keeping ability test (1) and the shape keeping ability test (2)were carried out for this sheet. The results are shown in Table 1. Inthe shape keeping ability test (2), a polypropylene container was usedas the lower container. This sheet was significantly poor in shapekeeping ability.

Comparative Example 2

[0091] Using polystyrene (H550 manufactured by Japan Polystyrene Co.Ltd., Tg=100° C.), a 0.3 mm thick sheet was produced by a tabletop pressmachine. The shape keeping ability test (1) and the shape keepingability test (2) were carried out for this sheet. The results are shownin Table 1. In the shape keeping ability test (2), a polypropylenecontainer was used as the lower container. This sheet was significantlypoor in shape keeping ability. Moreover, when the test piece bent in theshape keeping ability test (1) was recovered to the original conditionbefore bending, wrinkles occurred at the bent portion. TABLE 1 Tg Shapekeeping test (1) (° C.) after 10 sec. after 1 min. Shape keeping test(2) Example 1 34 165° 145°  70° Example 2 27 125° 90° 60° Comparative −1 5°  5°  5° Example 1 Comparative 100   30° 30°  5° Example 2

What is claimed is:
 1. A covering material having a layer formed of aresin of which glass transition oint is in the range of 10° C. to 50° C.2. The covering material according to claim 1 , wherein the resin isamorhous resin.
 3. The covering material according to claim 1 or 2 ,wherein the resin is a copolymer of (a) ethylene and/or α-olefin, and(b) cyclic olefin and/or alkenyl aromatic hydrocarbon.
 4. The coveringmaterial according to claim 1 , wherein the resin is a copolymer of (a)ethylene and/or α-olefin, and either of (b1) cyclic olefin or (b2)alkenyl aromatic hydrocarbon.
 5. The covering material according toclaim 1 , wherein the resin is a copolymer of (a) ethylene and/orα-olefin and both of (b1) cyclic olefin and (b2) alkenyl aromatichydrocarbon.